1. Field of the Invention
The present invention relates to a novel inkjet recording method and inkjet recording apparatus.
2. Description of Related Art
An inkjet recording mode is one for recording images and texts by flying minute droplets of ink to adhere onto a recording medium by various operation principles, and has advantages such as relatively high speed, low noise and easiness of multiple coloration. In the above inkjet recording mode, various improvements have been performed in various fields such as an ink, inkjet recording medium and inkjet recording apparatus, and at present, the mode has become rapidly popular for various fields such as various printers, facsimiles and computer terminals. In particular, recently high-quality picture technology in the printer has been improved, and its level has come at a picture quality of photograph.
As the inkjet recording apparatus used in the inkjet recording mode, for enhancing a printing speed, those where multiple ink jet openings (nozzle sections) and ink liquid paths are integrated as a recording head where multiple recording elements are integrated/arrayed (hereinafter also referred to as a multihead) are used. Additionally, as the inkjet recording apparatus for corresponding to coloration, those where multiple recording heads composed of the above configuration are comprised are frequently used. In that case, it is general that the recording heads which ejaculate inks of respective colors are disposed in parallel with a main scanning direction.
Here, when a color image picture is printed, differently from those where only characters are printed in a black-and-white printer, various factors such as color density, gradation and uniformity are important to obtain high-quality pictures. In particular, with respect to the uniformity, slight dispersion of nozzle units which occurs in difference of multihead fabrication steps influences jetting amounts and jetting directions of inks at respective nozzles, and becomes a cause which finally deteriorates image quality as uneven density of a printed image. Also, speed variation at a main scanning of a carriage where heads are loaded, variation of sub scanning paper feeding amount of the medium, and variation of a distance between a medium surface and a nozzle face on the medium cause deterioration of the image.
For the above problems, a so-called multi-pass recording method has been proposed where image deterioration due to the dispersion of respective nozzles and various variations is reduced by scanning multiple times the recording head having multiple nozzle sections onto the same recording area on the inkjet recording medium and forming an image according to a complementary thinning-out pattern. As a mask used in this case, as described in JP-Tokukaisho-60-107975A, the method of using a complementary pattern with a constant thinning-out rate of a certain rule is the commonest.
However, as described below, when using such a regular mask, conversely uneven colors, stripe unevenness and white spots sometimes remarkably appear, and thus, the method of using a mask pattern without regularity has been proposed as an improving countermeasure of this. By forming an image thinned out of this thinning-out pattern without regularity, it is possible to prevent the uneven density and uneven colors produced due to a synergistic effect of regularity of the image and regularity of the mask, and realize high-quality picture and high speed printing to some extent (For example, refer to JP-Tokukaihei-7-52390A, JP-Tokukai-2002-96461A, and JP-Tokukai-2002-144552A.).
Whereas, the present applicant has found that when a certain inks and a recording medium is used, and in particular when high-quality printing such as silver halide photograph is required, sufficient image quality is not obtained only by the proposed thinning-out printing method. This is illustrated below.
The inks used in the inkjet recoding mode are broadly divided into dye inks where color materials are dissolved in solvents and dispersion inks where color materials, mainly pigments are dispersed in solvents. The dye dissolves in the solvents and is in a molecular state or a cluster state, which makes its absorption spectrum sharp, and develops clear color with high purity. Additionally, there is no particle pattern due to particles and no scattered light and reflected light occur, therefore it is possible to obtain an inkjet image with high translucent feeling and clear color phase. The dye has a property excellent in scratch/abrasion resistance because no color material particle is present on the surface of media. The dye, however, has drawbacks of poor light resistance because dye molecules tend to break by photochemical reaction. The reduction in dye molecular number directly reflects upon a color density. It is an actual state that the inkjet recording image using the dye inks is the high image quality but the poor image stability against light, and the technology which is superior to silver halide photographs in the light of stability has not appeared yet.
As the method for solving this problem, pigment inks where the pigments with good light resistance are used as colorants have been used for the intended use where the high light stability is required.
In case of using such a pigment, increase of an ink adhesive amount generates aggregation of pigment and causes the problem that a color image with high quality and definition cannot be obtained. To solve such a problem, it is possible to apply a method for forming a color image by using an ink set in which special colors, such as red and violet, is added to inks of yellow, magenta, cyan and black (for example, see JP-Tokukai-2003-266913A).
However, when an inkjet image recording according to the thinning-put pattern without regularity is performed using the pigment inks, a dot position formed at each scanning has no regularity. Therefore, the case where the ink droplets of cyan, magenta, yellow and black are adjacently printed on the inkjet recording medium at the same scanning becomes frequent. As a result, the respective ink droplets are mixed one another, aggregation of pigment particles is caused, and a phenomenon called bronzing which is hardly caused in the dye inks occurs. A problem that the color image cannot be accurately reproduced occurs.
In particular, in order to form the image at high definition like a silver halide photograph, when the inkjet recording medium having a micro-porous layer containing inorganic fine particles with a mean particle size of 100 nm or less is used, an absorption speed of inks is fast and the aggregation of pigment particles present on the recording medium occurs more easily. Besides, it has been found that due to using the mask pattern without regularity, a probability that different color dots are adjacently printed becomes high, and the formation of image at high definition becomes difficult because the pigment particles having different color tone are mixed on the recording medium.
This is because when using the regular thinning-out pattern, the position of each ink formed on the recording medium at one scanning can be finely controlled and mixture of the dots can be effectively inhibited whereas it is difficult to perform such a control in the case without regularity.